Here are facts directly from the National Park Service's contingency plan, prepared in advance for the event of a government shutdown.
Services and programs that will be ceased
• All national parks will be closed and secured.
• Visitor centers and other facilities will be closed.
• Education programs and special events will be canceled.
• Permits for special events will be rescinded.
• Guests staying in hotels and campgrounds will be notified of the closure and given 48 hours to make alternate arrangements and leave the park.
Services and programs that will remain operational:
• Law enforcement including the U.S. Park Police and emergency and disaster assistance.
• Firefighting and monitoring.
• Border and coastal protection and surveillance.
• Limited management of ongoing projects that are funded from non-lapsing appropriations.
• Access to through roads.